1. Field of the Invention
The present invention relates to a process for preparing a high molecular weight organopolysiloxane from a low molecular weight organopolysiloxane.
2. Description of the Prior Art
As a method of polymerizing a low molecular weight cyclic organopolysiloxane or a linear organopolysiloxane to produce a high molecular weight organopolysiloxane, the following processes are known:
(i) a process in which starting organopolysiloxanes are reacted under predetermined reaction conditions by use of an alkali metal hydroxide or silanolate thereof as a catalyst, then a neutralizing agent is added to the resulting reaction mixture to neutralize the catalyst, and low molecular weight polymers are removed [see J. Am. Chem. Soc., 76,249 (1954)]; PA1 (ii) a process in which starting organopolysiloxanes are subjected to polymerization at a comparatively low temperature by use of a quaternary phosphonium hydroxide or silanolate thereof as a catalyst, then temperature is raised followed by heating for a predetermined period to deactivate the catalyst, and low molecular weight polymers are removed [see J. Polymer Sci. 40, 35 (1959)]; and (iii) a process in which starting organopolysiloxanes are reacted under predetermined reaction conditions by use of a strong acid, e.g. sulfuric acid, as a catalyst, then the resulting reaction mixture is admixed with a neutralizing agent or washed with water to deactivate the catalyst, and low molecular weight polymers are removed [see D. F. Wilcock, Gen. Elec. Rev., 49, [No. 11], 14 (1946)].
The above three processes, however, have drawbacks as follows.
First, the process of (i) above uses a large amount of catalyst for reaction, resulting in the formation of a large amount of salts upon deactivation of the catalyst after the reaction. Therefore, a purification filtration step for removing the large amount of formed salts imposes a heavy burden on the production, in regard of equipment, labor, energy, time and cost.
The process of (ii), on the other hand, has the drawback that the high molecular weight organopolysiloxanes obtained are poor in electrical insulation property and have an odor. In addition, where a plurality of organopolysiloxanes are used as starting material in order to prepare a high-molecular copolymer, only those copolymers in which structural units are arranged in block form can be obtained; namely, it is difficult to obtain a copolymer in which structural units are arranged at random. Further, where an organopolysiloxane having an amino group, mercapto group or the like is used as at least part of the starting materials, equilibration reaction does not take place satisfactorily and the resulting high molecular weight product will take a milky color.
The process of (iii) above, if carried out by use of a neutralizing agent, requires a large amount of neutralizing agent, leading to formation of a large amount of salts and to a great processing burden imposed by a purification filtration step for removal of the salts, as in the process of (i). Where the process of (iii) is carried out in the mode of washing the reaction mixture with water, there arise the problems of complicated production steps, low yield, and a heavy burden with respect to equipment, labor, energy, cost, etc. imposed by a treatment step needed for disposal of large amounts of waste water.